A conventional transmission way for the bicycle is to pedaling the pedals on the crank which rotates the chainwheel and the chain between the chainwheel and the rear sprocket which is fixedly mounted to the rear wheel hub so that the rear wheel rotates to move the bicycle forward. The rear wheel hub includes a hub, a driving socket fixed to an end of the hub and the rear sprocket mounted to the driving socket. When the chain rotates the rear wheel sprocket to rotate the rear wheel, the sequence of the transmission is the chain, the rear wheel sprocket, the driving socket, the hub and the rear wheel. The conventional rear wheel sprocket has a hole with multiple ribs extending axially from the inner periphery of the hole, and the driving socket has multiple grooves for receiving the ribs so as to connect the rear wheel sprocket to the driving socket. By the connection, the rear sprocket can transfer force to the rear wheel to move the bicycle forward.
In order to reduce the weight of the driving socket, the conventional driving socket is made by aluminum and the rear wheel sprocket is made by iron which is harder than the aluminum. The rear wheel sprocket is mounted to the driving socket by the engagement between the ribs and grooves so that the ribs made by aluminum are quickly damaged by the harder rear wheel sprocket. Besides, the hole of the sprocket is larger to the driving socket so as to be easily mounted to the driving socket, the gaps between the ribs and the grooves make wearing between the sprocket and the driving socket. The wearing makes the gaps to be larger and the larger gaps cause the pedaling to be mul-functioned which means no transmission force is generated and transferred to the rear wheel. Furthermore, the gaps generate noise during pedaling.
Taiwan Utility Model No. 096218930 discloses a hub 10, a driving socket 20 on one end of the hub 10 and a protection member. The driving socket 20 has an enlarged flange 22 on the side connected with the hub 10 and the multiple restriction ribs 211 and at least one positioning rib 212 are on the outer surface of the driving socket. The protection member is located on one side of the restriction ribs 211. The protection member has contact pieces 42 which are made by hard material and have the same amount of the restriction ribs 211.
As shown in FIG. 1 of Taiwan Utility Model No. 096218930, the protection member contacts the flange 22 and the restriction ribs 211 and each contact piece 42 has a ring 41 which is used to connect the contact pieces 42 and then the contact pieces 42 are connected to the driving socket 20 so as to protect the restriction ribs 211 from being worn out by the sprocket 30. However, each contact piece 42 contacts the restriction ribs and the flange by one side and a curved surface 421 thereof. The other end of the contact piece 42 is a free end. The distance between the free end to the ring 41 is so long so that a gap is formed between the free end and the restriction ribs 211. The gaps make the contact piece 42 cannot be matched with the restriction ribs 311. Once one of the contact pieces 42 is worn out severely, the whole protection member has to be replaced.
As shown in FIG. 4 of the Taiwan Utility Model No. 096218930, each contact piece 52 has a curved surface 521 and a protrusion 522 is located between adjacent curved surfaces 521. The driving socket 20 has recesses 213 for receiving the protrusions 522 so as to position the contact pieces 52 to the side of the restriction ribs 211. Although the restriction rib 211 is located on a side of the contact piece 52, the contact piece 52 is connected in radial direction from the outside of the driving socket 20 toward the center of the driving socket 20 and by the engagement between the protrusions 522 and the recesses 213. After being re-assembled and assembled several times, wearing between the protrusions 522 and the recesses 213 makes the contact pieces 52 cannot be matched with the driving socket 20 and even worse, the contact pieces 52 drop from the outer surface 21 of the driving socket 20 radially.
As shown in FIG. 5 of the Taiwan Utility Model No. 096218930, each contact piece 62 has a curved surface 621 which is matched with the outer surface 21 and each contact piece 62 has a thin guide surface 622 perpendicularly defined in a side which is located adjacent to the restriction rib 211. Each restriction rib 211 has a guide slot 214 which is located corresponding to the guide surface 622. The contact pieces 62 are engaged with the side of the restriction ribs 211 by the engagements between the curved surface 621 and the outer surface 21, and between the guide surfaces 622 and the guide slots 214. However, the contact pieces 62 contacts the restriction ribs 211 only by the guide surface 622, and the other side away from the restriction rib 211 does not have any restriction means to position that side, so that the contact pieces 62 are easily disengaged from the outer surface 21 in the direction that is away from the restriction ribs 211. When in assembling, the contact pieces 62 are respectively in contact with the side of the restriction ribs 211, the contact pieces 62 may drop from the tangent direction of the outer surface 21, so that the contact pieces 62 have to be re-assembled again.
The protection member can only protection one side of the restriction ribs 211 and when the rear wheel sprocket 30 rotates counter clockwise, the rear wheel sprocket 30 directly contact the driving socket 20 so that the other side of the restriction ribs 211 are worn out by the rear wheel sprocket 30. This protection member cannot be used for the bicycles with single rear wheel sprocket. Furthermore, when ridding on a rugged road, the vibration is transferred to the rear wheel hub and the rear wheel sprocket 30 directly contacts the sides of the restriction ribs that are not protected by the protection member, so that the driving socket is easily damaged and has to be replaced.
The present invention intends to provide a protection unit for a hub and the protection unit covers the three sides of the ribs.